LCD displays are widely used in TVs, notebook computers, PCs, mobile phones, and other electronic products with display function. In an LCD display, cold cathode fluorescent lamps (CCFLs), field-effect light-emitting devices (EL), light-emitting diodes, or other elements capable of emitting a visible light are used as a backlight. In recent years, LED has gradually been a preferred backlight source instead of CCFLs because it has many advantage including: long lifetime (about 100,000 hours), capable of optimizing color gamut, small size/design flexibility, driven by low-voltage power supply, quicker turn-on time, without an inverter, operated efficiently over a wider temperature range and so on.
An LED backlight device comprises an LED matrix for providing an LCD panel illumination. In order to make the LCD panel be illuminated with uniform light, and prevent bright spots being generated on the LCD panel, improving a lens which covers the LED so as to refract the light from LED is the mainly solution in prior arts. Therefore, in the LCD display using LEDs as backlight source, how to enhance the uniformity of brightness or make the light distribution be wider is the key point to improve the LED backlight device. For example, U.S. Pat. Nos. 7,348,723, 7,963,680, 7,621,657, 7,798,679, 7,866,844, 7,766,530, US Patent Publication No. 20090116245, U.S. Pat. Nos. 7,474,475, and 7,746,565 all disclose lenses or LED devices designed for an LCD panel.
A lens 13 and a light source device 1 shown as FIG. 1 is disclosed in U.S. Pat. No. 7,348,723. The light source device 1 comprises a light emitting element 11 mounted on a substrate 12 and the lens 13. The light emitting element 11 is disposed in a hemispherical recession 10 of the lens 13, and emits light thereby travelling within the lens 13 and then emitted from a light control emission face 130 of the lens 13. The light control emission face 130 includes a first light emitting region 130a and a second light emitting region 130b, wherein the first light emitting region 130a has a gently curved downward-convex configuration; the second light emitting region 130b extends around the first light emitting region 130a and has a gently curved upward-convex configuration. FIG. 2 is a diagram showing a distribution of emission intensity from the light source device 1. The light source device 1 generates a round light pattern with higher intensities in the paraxial region and lower intensities in the off-axis region.
However, although the light pattern generated by the light source device 1 gives lower intensities in the paraxial region, the light source device 1 still can't solve the problem of having bright dots in the paraxial region on the illuminated object. Moreover, in order to modify the uneven light pattern generated on the LCD panel, the light source devices 1 in a backlight module might have to be arranged closer to each other. Furthermore, due to the increasing requirement of thinner display monitors and a consideration of cost, such light source device 1 must be improved about increasing the light emission angle thereof to shorten the distance between the light source device 1 and LCD panel or to increase the distance between each light source device 1. However, significant light refraction by the light control emission face 130 generally increases a reflex flux, leads to the Fresnel's reflection phenomenon happened. That is, the total flux of the light emitted from the light control emission face 130 decreases. In addition, part of light emitted from the region where the incident angle is equal to the corresponding emission angle is overlapped each other thus outgoing light fluxes are concentrated, thereby causing of a ring-shaped bright line in the light pattern. In a result, the light source device 1 is hard to have both the perfect scattering ability and the perfect uniformity of scattering property. A light source device disclosed in U.S. Pat. No. 7,621,657 is similar to the light source device 1 disclosed in U.S. Pat. No. 7,348,723, it also has the shortcomings that the paraxial zone of the light source device is too bright and it is difficult to achieve the requirement of high scattering ability.
U.S. Pat. No. 7,766,530 discloses a light source device including an optical lens having a bell shape. However, this type light source device also generates a light pattern with higher intensities in the paraxial region. In addition, due to a concave surfaces of the lens make light away from the optical axis of the light source device be refract to further close to the optical axis; and a convex surfaces of the optical lens make the incident light be refract to further away from the optical axis, this type light source device has the shortcomings of uneven light distribution and deficient scattering ability.
For improving the scattering ability of a light source device, in the optical lenses of the light source devices disclosed in U.S. Pat. Nos. 7,963,680, 7,798,679, 7,474,475, 7,746,565, each light incident surface thereof has recession (or concave curve part) and each light emitting surface thereof has a concave part disposed at the center thereof and a convex part surrounding the concave part. Wherein, the optical lens disclosed in U.S. Pat. No. 7,963,680 has a light emitting surface including a cone-shaped central recession and a recession forming by a light incident surface being bullet-shaped with round top. However, such optical lens is still hard to achieve the requirement of making display monitors using the optical lens be thinner since the light pattern of these prior art is wider distribution cause lower intensities effect in the paraxial region. Otherwise, although U.S. Pat. No. 7,963,680 provided the optical lens to reduce the brightness of the paraxial zone of a light source device, in practical applications, light nearby the optical axis is strongly refracted by such optical lens, such that the light pattern projected by the light source device has a broadened center dark area. In a result, such optical lens is not applicable to use in thinner display monitors.
U.S. Pat. Nos. 7,474,475 and 7,746,565 disclose light source devices each including an optical lens having complicated optical surfaces, respectively. Both the optical lenses comprise a light emission surface having a recessed part rear the optical axis. Wherein, light incident on the recessed part is reflected to a refracting part being extended from the recessed part and forming a convex shape according to the total reflection effect. However, U.S. Pat. Nos. 7,474,475 and 7,746,565 are unable to provide even light pattern in practice, and such lenses are hard to process, and become thicker and low precision as its complex spherical surface.
Broadly speaking, optical surfaces are not portions of a sphere or plane called asphere, including asymmetric free-form surfaces. Because aspherical lenses have a significant effect in simplifying the structure of the optoelectronic devices, reducing the size and weight of the system, aspherical lenses are increasingly wide range of applications in the field of optoelectronic instruments.
If LED light source devices applied to a LCD display have design deficiency, they may cause the problems of bright dot, chromatism, requirement of high density lay-out or requirement of disposing other elements for promoting even light distribution. Wherein, when an LED light source device has a problem that the paraxial zone of the light source device is too bright, it may cause chromatism thereby affecting the color rendering of the LCD display. Besides, requirement of high density lay-out leads to increment of manufacturing cost, accumulation of heat and affects the device lifetime; requirement of disposing other elements further leads to increment of volume or weight of the LCD display. As LCD displays tends to be thinner, be realistic in quality and minimize cost, how to enhance the scattering ability, reduce chromatism and become thinner of an LED lens is the target that LED backlight module manufacturers anxious to improve.